1. Field of the Invention
The present invention concerns the manufacture of ophthalmic lenses from synthetic materials, for example thermoplastic materials.
It is more particularly but not necessarily exlusively directed to the case where the synthetic material is polycarbonate.
2. Description of the Prior Art
At this time polycarbonate ophthalmic lenses are injection molded or hot pressed.
The injection molding manufacturing process as described for example in French patent No 2 380 117 entails major investment; also, it is not applicable to the manufacture of thick ophthalmic lenses and, by virtue of the method of forming and cooling them, results in the presence within the ophthalmic lenses obtained of high internal stresses likely to compromise their optical qualities.
The hot pressing manufacturing process as described for example in French patent No 2 358 256 also entails major investment since, starting from a blank with parallel surfaces or a preformed crude lens, it requires not only an oven where the blank or crude lens is preheated but also a special press adapted to apply the final ophthalmic lens configuration to the crude lens at high temperature by the action of optically finished molding surfaces to which a specific molding force is applied, in practise horizontally.
Additionally, this hot pressing manufacturing process requires preheating of the molding surfaces and of the workpiece to be formed.
An object of the present invention is to provide a simple method of forming finished or semi-finished ophthalmic lenses free of any internal stresses at ambient temperature and without requiring major investment.